360 Mr. T. Tate on certain Modifications of the Form of 



proper acknowledgement of my sense of the value of Professor 

 Riess's many interesting researches in this branch of physics. It is 

 really with no view to a painful philosophical controversy that I 

 have been led to submit this paper for the consideration of the sci- 

 entific world, but solely with a view to a correct interpretation of 

 very important electrical phsenomena and the progress of elec- 

 tricity. 1 would also, as already observed, desire to obtain some 

 little consideration, in justice to myself, in reply to the rather 

 disparaging criticisms which j\l. Riess has been led to make on 

 my original researches, and which have been further and recently 

 repeated by M. De la Rive; and I especially invite the attention 

 of those engaged in electrical investigations to my several papers 

 referred to in this memoir. 

 Plymouth, April 5, 1856. 



XLIV. On certain Modifications of the Form of the new Double- 

 acting Air-pump with a Single Cylinder. By T. Taits., F.R.A.S.^ 



THE characteristic feature of the new air-pump, described in 

 the Philosophical Magazine for April 1856, consists in the 

 double piston acting in a single cylinder. For the sake of di- 

 stinction, I shall call this form of the pump No. 1. I have since 

 constructed this pump with different systems of valves, with the 

 view of determining the form which is most eligible for general 

 use. 



There is a little loss of dynamic effect in working the pump 

 No. 1, from the circumstance that one of the solid pistons forms 

 a vacuum on one end of the cylinder at every stroke ; but this 

 loss of work, or dynamic effect, is considei-ably less than that 

 which takes place in the common pump. In order to eliminate 

 this defect, I have placed valves in the pistons A and B, lifting 

 towards the corresponding ends of the cylinder. By this arrange- 

 ment the exhaustion is performed with the least possible expen- 

 diture of work or dynamic effect. This form of the pump, for 

 the sake of reference, I shall call No. 2, But this oeconnmic 

 construction is attended with a little loss of exhausting power, 

 owing to the greater amount of air which fills the valve spaces. 

 Whilst the exhaustion effected by No. 1 is measured by about 

 two-tenths of an inch of mercury, that of No. 2 is measured by 

 about four-tenths of an inch. 



Some persons, in my opinion without a sufficient reason, seem 

 to object to the piston passing the exhaustion orifice E. In 

 order to suit the views of such persons, I have constructed an- 

 other form of the pump, which I shall call No. 3, in which the 



* Communicaterl by the Author. 



